Method of carrying out melting processes



July 23, 1957 T. E. suEss ETAL 2,800,631

' METHOD oF CARRYING OUT MEETING RRocEssEs Filed Nav. 16, i955 H ISATTORNEYS United atent VMETHOD F CARRYHG QUT MELTING PROCESSES TheodorEduard Suess, Luxembourg, and Herbert Trenkler, Hubert Hauttmann, andRudolf Rinesch, Linz (Danube), Austria; said Suess assigner toVereinigte Osterreichische Eisenund Stahlwerke Aktiengesellschaft, Linz(Danube), Austria, a corporation of Austria Application Nov. 16, 1955,Serial No. 547,233

2 Claims. (Cl. 75-60) This invention relates to a process for thetreatment of metallic or metal-containing materials withoxygen-containing gases, preferably high purity oxygen, and hasparticular relation to a-process of this type in which fusible materialsare treated at high temperatures with said gases.- Stillmoreparticularly, the invention relates to a process for the refining ofmolten metal with high purity oxygen blown downwardly onto the surfaceof a bath of the molten metal.

The invention is particularly adapted to the refining of primarily hotmetal charges, for example, molten pig iron, but it is also applicableto the production of refined metals from solid charges, such as solidpig iron for the production of steel, as hereinafter set forth. Theinvention is also characterized by the fact that the heat required forthe refining' of the molten impure metal is autogenous, being producedprimarily by reaction of the oxygen gas with the impurities in themolten metal, although when utilizing solid charges of impure metal, theheat required for melting of the charge prior to refining is provided bycombustion of a suitable fuel with the oxygengas.

Processes for the utilization of high purity oxygen in the refining ofmolten metal charges, such as pig iron, have been suggested ever sincethe development of the original pneumatic process by Bessemer. Attemptsto blow with high purity oxygen in a conventional Bessemer or Thomasconverter through bottom tuyeres has resulted in the destruction of therefractory bottom within the short time of one heat. On the other hand,high purity oxygen refining processes have been previously proposedy inwhich the oxygen is directed onto the molten metal bath surface in theform of a jet or jets issuing from tuyeres positioned in the wall of therefining vessel above the melt line. ln such processes, the horizontalvelocity component of the oxygen jet at the melt surface causes thedevelopment of excessively high temperatures above and at the melt-slaginterface on the side of the vessel opposite the tuyeres or oxygen jetinlet so that a rapid deterioration'of refractory occurs. In addition,with such an inclined oxygen jet, a loss of oxygen efficiency resultsdue to defiection of the gas from the melt surface and burning of alarge proportion (40-50%) of the evolved carbon monoxide to carbondioxide above the melt, which is further undesirable in contributing tothe short refractory life. In addition, the heat produced by high purityoxygen-molten metal reactions is more than sufficient to provide theheat necessary for completion of the refining reactions to the desiredsteel analysis, and this large amount of additional heat developedwithin the refining vessel due to carbon monoxide combustion isundesirable. Further, in the utilization of high purity oxygen as therefining medium, the reduction in oxygen eficiency resulting from thiscombustion of the carbon monoxide with a portion of theoxygen feedcannot be tolerated.

Accordingly, it is recognized that the application of such processes, inwhich the molten materials, for example pig iron, are treated inrefining devices provided' with refractory linings are severely limiteddue to the extremely high temperatures developed by reaction of the highpurity oxygen gas with the molten metal and the short life of therefractory linings when exposed to such temperatures. This isparticularly true in those processes, such as production of steel, inwhich chemical reactions capable of causing corrosion of the refractorylining take place. Thus, in a device provided with refractory lining,such as a converter in the previously proposed processes when highpnrity oxygen is blown to the surface of a bath of molten pig iron, withor without a slag cover, combustion of the impuritiesrin the metal, andalso iron itself result in such extremely high temperatures that therefractory lining is attacked and-damaged to such extent that it must berenewed after a short period of use. The refractory materials known atpresent are unable to resist attacks and stresses of this kind unlessvthe lining is protected by the application of particular conditions fromdirect exposure to the strong heat developedby the high purityoxygen-molten metal reactions. Accordingly, although the advantages ofmolten metal refining with high purity oxygen have been recognized,particularly with respect to the reduced nitrogen ballast compared tothe air blown pneumatic refining processes, there remains no economical,commercially feasible process for rening ofmolten metal with high purityoxygen capable of providing long refractory life and high oxygenefiiciency. In particular, the deficiencies of the proposed processes,emphasize the lack of a high purity oxygen refining process for moltenpig iron" having the aforementioned advantages to provide an economical,

commercially feasible process for production of refined steel at leastequal in quality to that produced by the well known basic open-hearthprocess from' pig iron of widely varying chemical compositions.

It is accordingly one of the main objects of the present invention toprovide a process for refining molten metals by surface blowing withhigh purity oxygen, in which, owing to the particular conditionsemployed, the`efactory walls of the apparatus utilized in carrying outthe process are protected from undue corrosion by thev excessively hightemperatures developed and the chemical reactions taking place at suchtemperatures.

Another object of the present invention is to carry out' thetreatment ofmolten metals, and other molten materials by surface blowing with highpurity oxygen in such a manner that the reactions of the oxygen gas'with the constituents of the molten bath and the resulting hightemperatures, to the extent possible, are limited to an oxygen jetimpingement area removed from the refactory lining' of the reactionvessel.

It is also a primary purpose and object of this invention to provide aprocess for thev refining of primarily hot metal charges, that is,predominantly molten pig iron, with high purity oxygen gas in whichcontrolled refining at substantially theoretical oxygen eficiency isaccomplished.

A further object is to provide a process for refining of molten pig ironwith a surface blown high purity oxygen jet in which an exceptionallyhigh refractory life is obtained.

The invention also has as its object to provide a process of surfaceblowing molten pig iron with high purity oxygen in which the refiningreactions and oxygen impingement on the melt surface are controlled in amanner such that over-oxidation of the molten pig iron bath isessentially avoided.

It'is still another object of the invention to provide a high purityoxygen refining process which is applicable to pig iron of widelyvarying chemical compositions,

dinary basic open-hearth practice, as well as those of higher siliconand phosphorus content required for blowing in the acid Bessemer andbasic Thomas converter processes to produce steels having analyses andqualities at least comparable to that of basic open-hearth steels.Another object of the invention is to provide a high purity oxygenrefining process for production of steel of excellent quality at a highrate of production, substantially comparable to Bessemer or Thomasconverter practice, for example, a blowing time of from to 30 minutesfor charges of from 30 to 40 tons to carbon end points of 0.05% orbelow.

Further objects and advantages of the invention will be apparent fromthe following detailed description of the process and the appendeddrawing.

The process of the invention generally comprises refining the moltenmetal in a converter type or other suitable vessel with a high purityoxygen jet impinging vertically or approximately vertically on the meltsurface substantially at the central portion thereof by means of a blastnozzle or other suitable jet producing means under controlledconditions, hereinafter defined, to supply to the molten metal therequired amount of oxygen for completion of refining within apredetermined time, and to produce autogenous heat sufficient to insurecompletion of the refining and adequate temperature in the refinedcharge for subsequent handling.

It has been found that by suitable arrangement of the nozzle or jetproducing device, and operation thereof for the supply and introductionto the molten metal of the high purity oxygen gas, suitable design ofthe refractory lined refining device in which the process is conducted,and proper use of amounts of materials charged, the foregoing advantagesare obtained, including a very eiiicient protection of the refractorylining.

According to the process of the invention, the high purity oxygen jet isblown vertically, or approximately vertically upon thecentral portion ofthe surface of a bath of the molten metal, the jet havingV a diameterand static pressure at the point of origin, that is, at the blast nozzleor other jet producing means, and the point of origin (blast nozzle)being spaced from the bath surface, such that direct contact of theoxygen jet and the molten metal is established and maintained throughoutthe refining period without deep penetration of the molten metal bath bythe jet. In so operating, the area of jet impingement is controlled toproduce a relatively confined zone of direct oxygen to molten metalcontact with respect to the total surface area of the bath. It has beendetermined in application of the present invention to the refining ofpredominantly molten pig iron charges by means of high purity oxygen,that the jet blown onto the surface of the molten iron, as abovedescribed, under a relatively low static pressure at the point oforigin, for example, at the overhung blast nozzle, of from 5 to 2Satmospheres (about 75 to 375 pounds per square inch), preferably atabout 8 to l2 atmospheres (about 1l5-l75 pounds per square inch), withthe jet diameter at the point of origin or blast nozzle being about lmillimeter (1&5 inch) per ton of charge, and with the point of origin orblast nozzle spaced from the bath surface from at least 150 millimeters(about 6 inches) up to about 2000 millimeters (about 80 inches),produces a sufficiently high reaction velocity of the oxygen with thebath constituents to insure the development of autogenous heat at a ratesufficient to provide the heat required for completion of the refiningin a minimum of time, consistent with controlled temperature and controland development of other necessary and required.

process conditions, such as fluid slag, avoidance of overoxidation(undue loss of iron to the slag), and avoidance of slopping. The processconducted under these condin'ons avoids a deep penetration of the oxygengas into the molten bath which seriously impairs refractory life 4 atthe bottom of the refining vessel. In addition, the impingement area ofthe high purity oxygen on the central portion of the bath isolates therefractory walls of the refining vessel from the extremely hightemperatures which are developed by the direct reaction of the oxygenand the molten metal.

It has also been found, according to the invention, that the utilizationof suitable design of reaction vessel and the use of the proper amountof material charged results in a ratio of the depth of the bath to thesurface area of the bath which augments the protection afforded to therefractory lining of the refining vessel and is also beneficial to theprogress of the refining reactions to produce finished steels of lowimpurity content comparable to those produced by the basic open-hearthprocess. In carrying out the process of high purity oxygen refining of amolten bath of pig iron, the rening vessel is of such design and thecharge is of such amount that the ratio of the depth of the molten bathin meters to the surface area of the molten bath in square meters shouldbe from about 1 to 5 to about l to 28 in refining vessels of variousdesign or in terms of the ratio of depth to diameter of a circular bathbetween 1:2.5 and 1:19. In other metallurgical processes to which thepresent invention is adapted substantially similar ratios may be used.

Although it is not intended to limit the present invention to anyspecific theory of action or mechanism, it is believed that applicationof the oxygen jet substantially vertically or approximately verticallyupon the central portion of the bath surface brings about a fiow in themolten metal from the center of the surface of the bath downwardly andthen along the bottom of the refining vessel, and upwardly at the sidesof the vessel to the surface of the bath, so that portions of theunrefined metal are continuously presented to a localized center ofdirect oxygen reaction with the bath metal, while reacted or oxidizedportions of the bath move away from this reaction center. This apparentcirculation of the molten material is facilitated by shaping of thebottom of the device in its refractory lining in a uniformly curveddesign, preferably hemispherical or similar shape, so as to offer theminimum of resistance to the circulation.

Due to the very high affinity of oxygen for iron, initial contact of thehigh purity oxygen jet with the molten metal bath causes a rapidcombination of oxygen and iron to form FeO in the confined centralreaction zone. This is demonstrated by ignition of the oxygen and thepropagation of a visible ame within the first minute of blowing. Thisreaction, together with oxidation of impurity elements, such as siliconand manganese, develops extremely high temperatures in the zone ofdirect oxygen contact with the molten metal which approach the boilingpoint of iron, as demonstrated by the evolution of a fume containingiron oxide and manganese oxide. A portion of the iron oxide goes to theslag with the other oxidized elements and a portion diffuses into thebath under the influence of the bath circulation, so that Within thefirst three minutes of the blowing vigorous carbon combustion isinitiated due to the high temperatures developed by these reactions. Theensuing reaction of carbon with the FeO and directly with the oxygen gasin the confined direct oxidation zone causes rapid formation of carbonmonoxide and the formationvof this CO causes a strong boil or agitationof the bath, which augments the bath circulation to continuously presentunrefined metal to the oxygen gas reaction zone and to create aslag-metal emulsion. The oxygen jet thus contacts the emulsion of bathand slag components which presents a larger reaction surface and causesthe refining reactions to progress rapidly although the oxygen jet doesnot penetrate deeply into the molten metal bath and is confined to anirnpingement area at the central portion of the bath surface. Thisvigorous boiling action is opposed by the pressure of the oxygen jetonly in the area of impingement, and outside of this area it representsprimarily endothermic yae-,sooner reduction offFeO by carbon to'formtheV evolved carbon tmonoxide, which reaction thus reffectivelyencompasses ,ton converter, the average durability of the refractory-is' over 200 heats (foregoing in percentages by weight). By

comparison, in basic Bessemer practice utilizing air rather than highpurity oxygen, the removable converter bottom must be relined after only35 to 60 heats. In addition, the refractory life obtainable by theprocess of the invention surpasses that obtained in normally operatedopen- 'hearth practice in that in refining of a normal charge' by ,basicopen-hearth about 36 lbs. of refractory .brickfis consumed per ton ofsteel produced to which must be added some 40 pounds of sintereddolomite for fettling operations, whereas total refractory consumptionin the `instant process is only about 24 lbs. perton of steel'produced.This advantage is even greater when compared to oxygen lancing in anopen-hearth'fwhich:accelerates refractory consumption.

The further advantage of high oxygen eiciency is `obtainable accordingto the process Vof the invention -when the oxygen jet impinges on thelcentral portion ofthe moltenbath surface fromdirectly above, .that is,approximately vertically. Oxygen efliciencies calculated on the .basisofY total oxygen input compared to oxygen consumed in the bathreactionsis approximately 95%. This is demonstrated'by an average oxygenconsumption of only 57 normal cubic meters (measured at standardconditions .of temperature and pressure) per ton of vsteel -includingoxygen consumption for heating the converters after relining. Thiscompared with calculatedv or theoretical oxygen requirements for therefining of the 'various pig irons blown to steel Vanalyses set forthbelow represents about Ua 95% efcient utilization of oxygen. Inaddition, analvyses of waste gases effluent from the converteriin'dicatethat the carbon in the instant process burns almost v100% to carbonmonoxide, the analyses showing on the. average over 90% CO and lessthan10% CO2,indicating that the oxygen inputis not lost by burning with thecarbon monoxide above the melt withinthe refining vessel,'as

in the case' of low angle impingementfrom,tuyeresfpositioned in the sidewalls of the refining vessel. `Moreover, this is Va distinct advantagein the instant process, since the reaction 'of the oxygen with the meltprovides more A,than sufficient heat for the refining, and Yadditionalheat .by l. burning of the carbon monoxide to carbon .dioxide .above themelt is to be avoided. The potential heat units in the eiuent carbonmonoxide may be utilized in various .ways by subsequent burning.

As above mentioned, it is a characteristic of the process of theinvention that in the confined zone of direct oxygen .reaction at thesurface of the molten metal bath, 4the oxidation products of theimpurities in the pig iron, such as silicon and manganese, as well asthe oxidized iron .form an early fluid slag which is always very rich inoxides, that is, highly oxidizing. With the formation of the .slag-metalemulsion, the iron oxide reacts with the carbon ipresent in the bath,primarily outside of the direct oxygen- .metal reaction zone, and sincesuch slag-metal reactions are-endothermic, 'thetmolten bath ismaintained cooler inthe vicinityof the walls of the refining vessel orconverter. :For example in the formation of one kg. of FeO, by .directoxidation with the oxygen jet and absorbed-as .iron silicate .into theslag, 80 kg. calories of heat are developed. .An equal amount of heat isabsorbed outside -slag and lmetal bath ceases.

...of the confined centralvzone of direct oxidation as'the 'FeO -f (assilicate)is.ireduced .byf the carbon inthe bath, as one Aexample iofVslag .metal reactions occurring during the blowing.

This-formation of anearly highly oxidizing fluid slagis ofparticulanvaluey in basic'refning when the process is .applied -topig'iron of analyses usedin ordinary openhearthpractice, which-would notbe amenable to refining by either theacid Bessemer process due to thephosphorus content, or the basic Thomas process dueto the lackfofsufficient phosphorus. With the rapid heating of the slag `coverandmetalbath, the proper amounts of lime or lime supplying substance, such aslimestone, maybe addedl at therbeginnin'g of the blow and during theblow to insure formation and maintenance of a slag of sufficientvbasicity. Thus, the early fluid, basic and highly oxidizing slag-formed provides van accelerated rate of phosphorus and sulfur removalfromtthe "bath, leaving thenished steel `only -asingle slaggingoperation. With sulfur contents -in the pig iron of from 0.045 to 0.08%,the sulfurisfdevcreased to 0.02-0.025%, and on the lowerA range ofsulfur .in thepig iron to values aslow as 0.012%..

In' usual operations, from l to about 4.5% lime is charged to obtain.thei foregoing result,.depending upon the phosphorus content inthepigiron. In addition, all of the lime require- Vment may befadded duringinitial charging before blowing is started, particularly where thesilicon content of the pig KYiron,-which is one of the firstoxidized'elements, is sufficiently high. On the other hand, the lime maybe charged in increments/during the blow,'but witha sufiicient amountinitially charged to provide a Abasicity adequate to absorb thephosphorus.

Inthe normal range of phosphorus in pig iron of lbasic openahearthquality from about 0.1 to 0.35%, the required slag volume including thelime charge is advan- 1tageouslymuch lower than the slag volume inthe'bottom blown basic Thomas process. The iron content of the slagvaries from about 9 to 18%, with generally higher FeO content in the`slag at higher phosphorus contents in the pigiron, and also at lowermanganese contents. Accordingly, the lowerpercentage of slag, forexample, :11 to 12% comparedto about 22% in the Thomas process resultsin comparable or lower total iron content lostto the slag, even thoughtheFeO content of the slag may be higher than the usual 10% in the basicThomas process.

The process in its'preferred embodiment utilizes high purity oxygen, bywhich the term is meant oxygengas analyzing at least 97% O2. For minimumnitrogen content in the finished steel of at least 98% oxygen andl pref--Yerably 99% or higher should be utilized. The frequency curves Abasedon produced steel analyses indicate that oxygen of at least 98% purityprovides a peak ormaximum at a nitrogen content of from 0.002 to 0.003%,with of all heats blown'showing a nitrogen contentof 0.004% or less.

The vigorous boil, above mentioned, continues up -to the carbon Aendpoint, and together with the induced cir culation of the bath metaltoward and away from the central zone of direct oxygen reaction,effectively counteracts any tendency to overoxidation of the bath. Whenthe llame dies and carbon combustion is completed, the bath becomesrelatively quiet and intimate contact between The turbulence of the bathand slag due to the oxygen stream impinging from directly above isinsufficient to cause continuance of oxygen-metal reactions. As aresult, steels blown by the process ofthe .invention do-not `suffer fromthe deteriorating effects of high oxygen (FeO) contents..Directfoxygendetermination Vby thehot extractionmethod yielded oxygenconvtents of 0.04% maximum for heats that were blown to a carbon endpoint of from 0.05 to 0.10% C. Thus, the oxygen content of steelsproducedy by the high purity oxygen blowing process compare veryfavorably with oxygen contents of basic open-hearth steel in the samecarbon range, and are definitely lower in oxygen content than bottomblown Bessemer steels using air, oxygen enriched air, oxygen and steam,or other gas mixture. f

As in the basic Bessemer process, the silicon is rapidly eliminated.However, in contrast to the basic Bessemer process, the use of highsilicon charges presents no problern due to the fact that slopping isnot encountered in the process of the invention to any degree similar tothat in the bottom blown Bessemer practice. In fact, higher silicon pigironspactually are advantageous in the high purity oxygen blowing due tothe heat producing effect of this element in the early stages of theblow with the result that higher scrap charges can be made in theprocess.

Regarding scrap additions, the process advantageously may utilize scrapcharges of up to about 30%, depending primarily upon the silicon contentof the pig iron, and also on the temperature of the hot metal charge.For lower ranges of silicon, such as 0.3 to 0.7% scrap charges of from10 to 15% are permissible. With silicon in amounts from 1 to'1.2%, scrapcharges of 20 to 25% may be utilized.

In general, the manganese content of the fully blown metal and of theslag increases with the total manganese content (pig iron and scrap).However, it is a characteristic of this oxygen steel making process thatthe high temperatures Vdeveloped in the reaction zone between the bathmetal and the slag cause a rereductionrof manganese from the slag intothe bath during the latter portion of the refining period. In the lastminutes of the blow, the manganese content in the bath again decreasesas the carbon drops to its final value, that is, at a normal end pointof 0.04-0.06. Accordingly, the manganese content in the finished steeland in the slag is subject to some control, and is governed by slagcomposition and volume, temperature and final carbon content. With theuse of a minimum amount of slag rich in iron oxide, for example only 70kg. per ton of steel, the amount of loss of manganese to the slag byburning may be considerably reduced. As above mentioned, extensive testshave shown that the amount of slag can be kept considerably lower thanthe conventional pneumatic process, such as the Bessemer and Thomasprocesses. Under these conditions of high developed temperature in therefining process and low slag volume with high iron oxide content,

a finished steel containing manganese in quantities at f least 10 timesthe amount of carbon, for example, 0.6 to 0.8 Mn at carbon end points of0.05% are obtainable. Accordingly, it is possible to pour rimming steelsdown to relatively -very low carbon contents without any addition of:manganese and deoxidizing agents. Under actual voperating conditionsthe best practice for production of A'standard grades is to refine downto 0.06-0.08% C and to `recarburize in the ladle. This practice resultsin a manganese content of from 0.6 to 0.8 and eliminates the necessityfor manganese additions to conform with the usual analysisspecifications. The above manganese content easily compares with theconventional composition of rimming low-carbon open-hearth steels, infact such 'analyses are near the upper limit of the range. It is alsopossible to catch the heat at higher carbon contents, so that theresulting content in manganese will be of a higher order than isnormally encountered in rimming open-hearth steels of identical carboncontent. Thus, it is possible to produce rimming low carbon high purityoxygen blown steels of a predetermined strength which is based on aninherently higher manganese content of -the heat.

It has also been found that a steel containing 0.1% 'carbon and as highas 1.5% manganese may be obtained, for example -by the additionvof-ordinary blast furnace ferrman'ganeSe, e. g., 15 kg. of 48%Ablastrfurnace ferromanganese per ton suces, and results in an increaseof Yabout 0.05 in the carbon content. VIn normal steel making operationsit was not previously possible to obtain such steels without the use ofexpensive refined ferromanganese products. Steels of such analyses, notonly exhibit increased toughness and yield strength but otherproperties, such as pressure weldability, are improved.

To exemplify the high manganese recovery in the steel withoutferromanganese additions after the blow, the results of the followingheats are provided. As indicated above, since the manganese content,under otherwise equal lconditions, increases in the finished steel withincrease in pig iron, it is to be noted that particularly high manganesecontent pig irons were employed. Nevertheless, it is evident that due tothe extremely high temperatures developed in this high purity oxygenprocess, a manganese recovery is possible which cannot be reproduced inknown processes.

Heat No. 1.--Pig iron analysis: 4.16% C, 3.02% Mn, 0.14% Si, 0.074% P,0.040%V S. Last converter control test (without ferromanganese ordeoxidizers): 0.09% C, 0.96% Mn, 0.005% Si, 0.039% P, 0.013% S, 0.007%

Heat No. 2.Composition of pig iron: 4.30% C, 3.24% Mn, 0.33% Si, 0.072%`P, 0.034% S. Last converter control test (without ferromanganese ordeoxidizer): 0.08% C, 1.02% Mn, 0.005% Si, 0.037% P, 0.010% S, 0.004%N2.

Heat No. 3 Composition of pig iron: 4.21% C, 2.88% Mn, 0.27% Si, 0.076%P, 0.044% S. Last converter control test (without fcrromanganese ordeoxidizer): 0.07% C, 0.93% Mn, 0.005% Si, 0.037% P, 0.012% S, 0.004%N2.

From the foregoing test, it may be seen that manganese recovery at least10 times as high as the final carbon content in the finished steel isobtainable by the process of the invention utilizing pig iron havingmanganese on the order of 3%.

In regard to output, the combustion of the impurities of the pig ironand the iron content of the slag total a loss of about 8.0% with anadditional 0.8% of iron lost in the dust fume from the process. Withmechanical losses averaging about 0.8%, the percentage recovery of therefining process is approximately 90%, comparable to the yieldobtainable by the basic open-hearth process. In the progress of the highpurity oxygen blowing, up to about the eighth minute, oxidation of theiron progresses under formation of comparatively large amounts of FeO,which, as above stated, promotes a desirable quick liquefaction of thebasic lime slag. At this stage in the blow, the slag shows maximumvalues of from 25-30% FeO. In the further course of the processreduction of Fe from the slag occurs which continues until the carboncontent of the bath of about 0.07 is reached. The FeO in the slagdecreases to about 10-12%. On further removal `of carbon, the FeO in theslag again increases so that in the final slag generally an iron contentaveraging 14% is obtained, and only at very low carbon heats does theiron content exceed this value.

Under these known metallurgical conditions above set forth, the totaloxygen requirement is calculated on the basis of oxygen pick-up of theheat during the rening period. summation of these oxygen gas volumesrequired for the oxidation to complete refining indicates substantiallya straight line function on oxygen input, and corresponding to thisrelative constancy of oxygen input, the oxygen pick-up proceedsuniformly dun'ng the blow. The oxygen input is maintained at a rate suchthat the speed of the refining process insures satisfactory rereductionof FeO from the slag, in the manner set forth above. In actual practice,based on experience in operation of 30 ton converters, oxygen feed ratesmay be mainltained such that depending upon pig iron analysis, amount ofscrap addition and desired finished steel analysis, the

refining to usual carbonend points on thehorder of.0.05`% C iscomple'tedsin-V from about-15 toabout 30 minutes, preferably. 18 to22minutes. Flow rates offrom about 4000vto8000-cubicmetersof oxygen`perhour are representative'of the oxygen input under these conditions.

In such* exemplary commercial Apractice with 30 ton converters chargedto 35 to 36 tons, oxygen pressuresfat the blast nozzle of about 8 to l0atmospheres and oxygen jet or blast nozzle diameters of from about. 27.5to 35 millimetersr( 1.11to` 1.4 inches) with' nozzle spacings varyingfrom 25 to 50-nches (about 650 to 1250 millimeters havebeen`- used, thepreferred spacing being from 30 to 40 inchesf(about 750101000millimeters). In general, it may be statedthatasthe oxygen pressure andnozzle diameter aren increased, the nozzle spacing is alsoincreased,.forexample, asthe capacity of the rening vesselandtotal-chargefis increased. Under these conditions,deepvpenetration-of themolten metal bath is avoided, while thenecessarydisplacement of `the slag. cover to maintainrdirect oxygen to moltenmetal contact is insured. However, infftheunusual circumstances ofanabnormally stlfslagzcover, the blow may be initiated using mechanicalmeans for penetrating the slag cover to establish oxygen tor metalcontact.`

It-is to` benoted,A that `in certain instances particularly wherethe-rateoffoxygen `input `is relatively high, that is, thei-totalL-blowingVtime is in the lowerportion of therange aboVestated, the pressure'of theoxygenV jet at theblast nozzle may be `reduced in the last few minutesof the blow to reducefthe rate= of oxygen input, which is benecial insupportingythe inherent characteristic ofthe process in regardtoavoidance of'over-oxidation of the heat. Due to this characteristicofthe process, it is generally unnecessary to utilize any deoxidizingagents such as ferromanganese and-ferrosilicon in the'production ofsemi-killed steels,

and only in the production of killed steels are the conventionaldeoxidizers employed.

Therprocess has as one of itsmajor advantages the applicabilitytopigiron of analyses' used in ordinary open-hearth'practice, whichwould-not be amenable to refining by;eitherV the acid Bessemerprocessor-the basic Thomas process. In addition, the process is fullyapplioable to pig irons"havin`gfanalyses of the type which are normally.utilizedin either the acid Bessemer or basic Thomasl'processes'.ATypicalillustrationsof the followingjspig-.irofns and the finishedsteels produced 'therefrom indicate that the process produces steelscomparable to open-hearth quality from pig irons of widely varyingphosphorus and silicon contents.

(1) 4.0% C, 1.5-2.0% Mn, 0.7-1.2% Si, 0.1-0.24% P, 0.05% S, and 0.01% Nblown to -a nished steel of the following analysis: 0.06% C, 0.35% Mn,0.00% Si, 0.026% P, 0.025% S, and 0.0025-0.0035% N (oxygen about 98%).

(2) Pig iron analyzing 3.6-4.25% C, 1.4-3.2% Mn, up to 0.3% Si,0.06-0.1% P, 0.04-0.07% S, and 0.01% N from which steel of the followinganalysis is obtained: 0.06% C, 0.35% Mn, 0.00% Si, 0.01-0.02% P, 0.022%s, and cool-0.002% N.

(3) Illustrative of a grade of pig iron falling between that of normalopen-hearth analysis and basic Bessemer pig iron is the following: 3.61%C, 2.16% Mn, 0.46% Si, 0.856% P, 0.062% S. Blowing of such a charge ofrather unfavorable chemistry by the process of the invention yielded asteel of the following composition: 0.04% C, 0.15% Mn, 0.0% Si, 0.014%P, 0.045% S. Clearly, such a pig iron would be definitely unsuitable forbasic Bessemer (Thomas) process rening, and would also presentconsiderable difliculty if used for open-hearth rening.

The accompanying drawing dagrammatically illustrates a device forcarrying out the present invention. In this drawing, reference numeral 1denotes a metallic wall and 2 the refractory lining of the refiningvessel. An oxygen supply lance 3 is centrally positioned and overhungabove the charge and is provided with a nozzle 3' for theintroduction'of rtheoxygen gas, -insertednsatl opening-of the cover 4;Thematerial charge, including molten pig iron, melted scrap, and slagforming. additions, such as limestone, isindicated at 5 and thedepth anddiameter of the-'upper surface-of the moltenbath` in the quiescentstateare'denoted byfH and D, respectively.- The lance 3 is retractable,and is provided withwater cooling ducts andconnections (not shown). Thelcooling water in actual practice is supplied to the-lance' at Iapressureof from 4 to 6 atmospheres andthe-normal owI rate is about 36 to 40cubic meters per hour. Under such conditions the temperature of thecooling water increases from approximately 14 centigrade input toavmaximum of about 30 centigrade in the effluent from the lance.

In the preferred commercial vpractice of the invention; a convertershaped vessel with an open mouth-'is .usually provided, through whichthe lanceisinserted into and rea tracted from operating position,asindicated inthecxample set forth below. In this manner, suitablelgas:take: olf devices may be` positioned at the throat of the convertertypevessel to collect the olf gases and separate,the'particir` late fumetherefrom.

The following isa detailed description af a typical operation oftheprocess, which is not to' be regarded asa limitationr-on theI invention,butrrrather as a completespecic embodiment thereof.

Example 1 i A closed bottoml converter of normally 30 tons (metric)capacity is charged with'. a total of about 36.tons of metal. through anopen mouth. The oxygen lance is.inserted through the mouth of theconverter to `thev adjusteddis` tance above the Vmelt surface. Thediameter. of the` sur'- face of the bath with sucha charge is about 5meter-sand the depth of the bath about l meter. A typical cycle ofoperations is given below on a time tarde-basis.V

Hours. 7100 kg. plant return vscrap charged toconverter 29,600 kg. pigiron pouredY from mixer into converter having an analysis asfollows:4.04%

C, 0.99% Si, 1.73% Mn, 0.153% P, and

0.045 S Addition of 850 kg. limestone andf K60- kg.`

bauxite v Introduction of nozzle, .oxygen .jet initiated -at a nozzlepressure of: 10 atmospheres (147 p. s. i.) with' a nozzlespacingabovethebath of 1000 millimeters 0.15 850 kg. limestone and 200kg. rolling mill iron slag added 750 kg. limestone chips added in fiveparts of kg. each Oxygen pressure reduced to 8 atmospheres--- Mouthflame transparent, nozzle withdrawn,

oxygen supply turned off-end of blowing time at 19 minutes Convertercontents sampled and analyzed as follows: 0.05% C, 0.00% Si, 0.31% Mn,

0.024% P, 0.02% S Slag drawn off 150 kg. Spiegel iron added to contentsof converter Slag remaining in converter stfened with 30 shovelfuls oflimestone 0.39-0.42 Steel poured into pan, temperature measured at 1575C., 6 kg. electrollour added to pan 0.42-0.45

Final test analysis on pouring into ingot mold was:

aio-0.13

0.07% C, 0.32% Mn, 0.022% P, 0.020% S, 0.0035% N.

11 t .t .i The process of the present invention may be also applic'd tothe production of metals, for example, production of steel, from solidstarting materials.V VIn the production of steel, pig iron and scrapiron, and if desired certain alloys andv fuels, such as coal or wood,are introduced into the refining vessel. Asr materials for producingheat for melting, coke, ferrosilicon, calcium carbide, aluminum `alloysand the like, which arer converted into slag or gaseous products at theprevailing refining temperatures can be added; The total amount of thestarting material mixture may be introduced as a single charge prior toinitiation of the melting, or may be gradually fed in small incrementalamounts. Suiicient fuel should be present for producing the combustionnecessary to provide the heat of fusion of the solid charge. Afterignition of the fuel, melting of the initial mixture is brought about bythe action of the oxygen jet.

The melting procedure is started by means of an ignited body which isintroduced immediately prior to the initiation of blowing of the oxygenjet, and is preferably positioned at that portion of the solid chargewhere the oxygen jet comes in direct contact therewith.

Thus, according to the present invention, a steel may be produced with aminimum consumption of fuel, for foundries or rolling mills, by meltingthe iron to be converted into steel with low grade fuel and a highpurity oxygen jet blast, for example, in cupola furnace, or in aconverter type vessel itself, and subjecting the thus melted solidcharge to high purity oxygen refining in the above described manner in asuitable refining vessel, such as a converter. In carrying out such amelting and rening treatment with high purity oxygen, the energyconsumption is extremely low, amounting to only 100 cubic meters ofoxygen (measured at standard conditions) per ton of steel produced. Ofcourse, as indicated above in the reining of primarily hot metal chargesconstituting pig iron with analyses as set forth above to refine steelsof 0.05% carbon content and analyzing as above indicated, the averageoxygen consumption is only about 57 cubic meters per ton (measured atstandard conditions).

The present process of surface blowing with high purity oxygen is alsoapplicable to the desulfurization of coprous materials and to theproduction of glass in the converter with the use of sodium chloride.Furthermore, the process is applicable to the treatment of blast furnaceslag to 45 the elimination of sulfur and conversion of slags into meltedcement or glass-like materials of the type used for the manufacture ofslag wool.

This application is a continuation-impart of my copending applicationSerial No. 206,147, iiled January 16, 1951, now abandoned. It will beunderstood that the present invention is not limited to the specificmaterials, steps and other specific details described above and may becarried out with various modifications without departing from the scopeof the invention as defined in the appended claims.

VWe claim:

1. Method of reiining molten impure iron in the presence of a slag in avessel having a refractory lining by blowing with oxygen, whichcomprises discharging a stream of oxygen vertically downwardly throughthe slag layer onto and below the surface of the bath at the centralportion thereof, to an extent to avoid material agitation of the bath bythe oxygen stream, the contact of the oxygen with the bath resulting inreaction of the oxygen with a portion of the iron and with theoxidizable impurities of the bath in a localized reaction zone spaced asubstantial distance from the refractory lining, the reactions in saidzone resulting in refining of the iron and gas evolution and in theproduction of high temperature in the reaction zone away from therefractory lining, said reaction producing a circulatory movement in themolten metal, which circulatory movement brings those portions of themolten metal bath which are remote from the reaction zone into thereaction zone whereby those portions are subjected to said reaction withminimum injury to the refractory lining.

2. The gaseous oxygen process set forth in claim l in which the oxygenis blown into said vessel under pressure in a range between about ve andabout twenty-tive atmospheres above normal atmospheric pressure.

References Cited in the tile of this patent UNITED STATES PATENTS1,032,653 Brassert Iuly 16, 1912 2,515,631 Cheswik July 18, 19502,598,393 Kalling et al May 27, 1952 2,741,555 Cuscoleca et al Apr. 10,1956 FOREIGN PATENTS 623,881 Great Britain May 24, 1949 642,084 GreatBritain Aug. 30, 1950 983,098 France Apr. 9, 1948

1. METHOD OF REFINING MOLTEN IMPURE IRON IN THE PRESENCE OF A SLAG IN AVESSEL HAVING A REFRACTORY LINING BY BLOWING WITH OXYGEN, WHICHCOMPRISES DISCHARGING A STREAM OF OXYGEN VERTICALLY DOWNWARDLY THROUGHTHE SLAG LAYER ON TO THE BELOW THE SURFACE OF THE BATH AT THE CENTRALPORTION THEREOF, TO AN EXTENT TO AVOID MATERIAL AGITATION OF THE BATH BYTHE OXYGEN STREAM, THE CONTACT OF THE OXYGEN WITH THE BATH RESULTING INREACTION OF THE OXYGEN WITH A PORTION OF THE IRON AND WITH THEOXIDIZABLE IMPURITIES OF THE BATH IN A LOCALIZED REACTION ZONE SPACED ASUBSTANTIAL DISTANCE FROM THE REFRACTORY LINING, THE REACTIONS IN SAIDZONE RESULTING IN REFINING OF THE IRON AND GAS EVOLUTION AND IN THEPRODUCTION OF HIGH TEMPERATURE IN THE REACTION ZONE AWAY FROM THEREFRACTORY LINING, SAID REACTION PRODUCING A CIRCULATORY MOVEMENT IN THEMOLTEN METAL, WHICH CIRCULATORY MOVEMENT BRINGS THOSE PORTIONS OF THEMOLTEN METAL BATH WHICH ARE REMOTE FROM THE REACTION ZONE INTO THEREACTION ZONE WHEREBY THOSE PORTIONS ARE SUBJECTED TO SAID REACTION WITHMINIMUM INJURY TO THE REFRACTORY LINING.